Hydraulic machine

ABSTRACT

A hydraulic machine having a variable intake volume/pump capacity includes working spaces ( 8 ) disposed in a cylinder ( 2 ), each of the working spaces ( 8 ) being limited by a piston ( 6 ) and a cylinder bore ( 4 ) in which the piston ( 6 ) is accommodated. The pistons ( 6 ) are supported on a reciprocating element ( 14 ) that rotates relative to the pistons ( 6 ), and therefore when the cylinder ( 2 ) rotates relative to the pistons ( 6 ), the pistons ( 6 ) undergo a displacement that determines the volume of the working spaces ( 8 ) which can be connected to high pressure and low pressure, to a control unit for actuating the valves ( 16, 22 ) as a function of the displacement of the particular piston ( 6 ), and to an angle-of-rotation sensor ( 36 ). The angle-of-rotation sensor ( 36 ) has a Gray code track ( 60 ) and an incremental track ( 58 ), to each of which at least one sensor ( 72, 74 ) is assigned.

CROSS-REFERENCE

The invention described and claimed hereinbelow is also described in DE102009049354.9, filed Oct. 14, 2009. This German Patent Application,whose subject matter is incorporated here by reference, provides thebasis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d).

BACKGROUND OF THE INVENTION

The invention relates generally to a hydraulic machine. Morespecifically, the present invention relates to a hydraulic machinehaving a variable intake volume/pump capacity, the rotational angleposition of which is detected using an angle-of-rotation sensor thatincludes a Gray code track and an incremental track

Valve-controlled hydraulic machines of that type are known, for example,from EP 1 537 333 B1. That publication describes a hydraulic machine ofan axial-piston design or a radial-piston design, which can be operated,in principle, as a motor or a pump, it being possible to adjust the pumpcapacity or intake volume in a nearly stepless manner via valve control.In one embodiment that is described, the hydraulic machine is designedas an axial piston machine, wherein a large number of pistons disposedin a cylinder is supported on a rotatably supported swash plate. Via theassigned cylinder chamber, each piston limits a working space which canbe connected to a pressure-medium inlet or a pressure-medium outlet viaa low-pressure side valve and a high-pressure side valve.

According to the known solution, the two valves are designed aselectrically releasable or blockable non-return valves which can becontrolled using the pump control unit and are operated in theparticular working space in the “full mode”, “partial mode”, or “idlemode”. As a result, the pump capacity or intake volume can be adjustedfrom a maximum value to 0 in a nearly stepless manner. Using the controlunit, the valves are controlled according to a control algorithm tominimize the pulsations of the total displacement (pump) or the totalintake volumetric flow (motor). The volumetric flow rate is oftenadjusted using phase-angle control, but can also be adjusted usingphase-section control or phase cut-out control.

Hydraulic machines of that type are also known, for example, from WO2008/012577 A2, WO 2008/012586 A1, or WO 2004/025122 A1. In all of thesehydraulic machines, the valves are controlled for example as a functionof the displacement of the particular piston, which, in turn, depends onthe angle of rotation of a drive shaft or output shaft which, by way ofexample, in the case of an axial piston machine, is operativelyconnected to the above-mentioned swash plate.

According to the known solutions, the angle of rotation or therotational speed is measured using angle-of-rotation sensors, in thecase of which a sensor is operatively connected to an incremental track.That is, according to these solutions, a track is formed, for example,on the outer circumference of the drive/output shaft or the rotatingcylinder, the track being embodied as recesses in a regular formation,similar to a gear wheel, and generating a sensor signal during rotation,for example, by changing a magnetic field, the sensor signal being usedto determine the relative rotational angle position. The track is oftenalso provided with an identification that can be used to detect areference position. The disadvantage of these solutions is that thelevel of accuracy and resolution that can be achieved does not fulfillthe requirements for the control of a hydraulic machine (DDU) accordingto the invention. Furthermore, the sensors often operate using opticalprocedures, making it practically impossible to situate them in themedium to be pumped.A further disadvantage is that up to one revolution must be completed todetect the reference position when using this incrementalangle-of-rotation measurement procedure.

SUMMARY OF THE INVENTION

In contrast, the object of the invention is to create a hydraulicmachine, in the case of which the rotational angle position of arotating component, for example, a cylinder drum or a drive shaft oroutput shaft, can be detected with high accuracy.

According to the invention, the hydraulic machine is designed as a DDU(Digital Displacement Unit) and comprises a large number of workingspaces disposed in a cylinder, each working space being limited by apiston and a cylinder bore in which the piston is accommodated. Thepistons are supported on a reciprocating element that can move relativeto the pistons, and therefore the pistons are displaced in the cylinderbore due to the motion of the cylinder relative to the reciprocatingelement that supports the pistons. Each working space can be connectedto high pressure or low pressure via high-pressure valves orlow-pressure valves, respectively. The hydraulic machine has a controlunit for selectively actuating these valves, and an angle-of-rotationsensor for detecting the rotational angle position of the cylinder orthe reciprocating element. According to the invention, theangle-of-rotation sensor is designed to include a Gray code track and anincremental track, to each of which a sensor is assigned.

The use of a conventional incremental track and an additional Gray codetrack enables the absolute angle of rotation to be detected with a highlevel of accuracy. This angle-of-rotation sensor does not requirereferencing, in contrast to the incremental sensors described initially.The design according to the invention therefore makes it possible todetect the rotational angle position and, therefore, the displacement ofthe particular piston in an extremely exact manner, and to control thelow-pressure valves and high-pressure valves as a function of thisposition and the desired pump capacity/intake volume.

According to an embodiment of the invention, the tracks are located onthe circumference of a base body, and the sensors of theangle-of-rotation sensor are distributed accordingly along thiscircumferential section.

The angle-of-rotation sensor can have a compact design when the twotracks are offset in the axial direction. The assigned sensors are thensituated accordingly.

To improve the resolution of the rotational angle measurement, aplurality of sensors can be assigned to one track. According to aspecific embodiment, five sensors are assigned to the Gray code track,and one sensor is assigned to the incremental track.

According to a variant of the invention, the incremental track isprovided with more track sections than is the Gray code track. A varianthaving 72 track sections of the incremental track and 36 track sectionsof the Gray code track has proven suitable; the ratio of track sectionsis therefore preferably 2:1.

In the case of a hydraulic machine, the base body on which the tracksare located is supported on a drive shaft or output shaft of thehydraulic machine. Basically, however, the two tracks can also be formeddirectly on the rotating component.

The sensors can be accommodated in a separate holder on the housingside, being inserted in a corresponding recess in the housing.

The design of the hydraulic machine is particularly simple when the twotracks are situated in the pressure medium.

It has proven effective in particular to use magnetic angle-of-rotationsensors instead of optical sensors. Magnetic sensors of that type can bedesigned e.g. according to the Hall Effect or, generally speaking, asmagnetostatic sensors.

In the case in which the tracks run in the pressure medium, it ispreferable to seal the sensors against the pressure medium.

In the case of an embodiment having a very simple design, the base bodyon which the tracks are located is fastened to an end section of thedrive shaft or output shaft, and is covered by a housing cover.

The hydraulic machine can be of an axial-piston design or aradial-piston design.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is explained in greater detailbelow with reference to schematic drawings. They show:

FIG. 1 a highly schematicized depiction to explain the operating methodof a valve-controlled hydraulic machine having a digitally variableintake volume/pump capacity (DDU);

FIG. 2 a detailed depiction of an angle-of-rotation sensor of thehydraulic machine shown in FIG. 1, and

FIG. 3 tracks of the angle-of-rotation sensor depicted in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the operating method of a valve-controlled hydraulicmachine 1 having a digitally adjustable pump capacity/intake volume(DDU) will be explained with reference to FIG. 1. In the embodimentshown, hydraulic machine 1 is designed as an axial piston machine inswash plate design, wherein FIG. 1 shows a highly schematicized variant.Only the essential components that are required to understand theinvention will be explained in the following. Reference is made to theabove-described prior art for more detailed designs. In the descriptionthat follows, hydraulic machine 1 is operated as a hydraulic motor,although the descriptions of the hydraulic motor basically likewiseapply to a pump having a variable pump capacity. As mentioned initially,the hydraulic machine is in no way limited to the axial-piston design.

According to the schematic depiction shown in FIG. 1, hydraulic machine1 includes a cylinder drum 2, in which a large number of cylinder bores4 is formed, each of which contains an axially displaceable piston 6.Together with cylinder bore 4, each piston 6 limits a working space 8,the volume of which is dependent on the displacement of piston 6. Eachpiston 6 bears via a piston shoe 10 against a slanted swash plate thatis connected to output shaft 12. Control curve 14 formed by the rotationof the swash plate is shown in the depiction in FIG. 1; control curve 14shows how the piston displacement and, therefore, the volume ofparticular working space 8 are dependent on the angle of rotation. Asshown on the right in FIG. 1, each working space 8 is connected via aninlet valve 16 to a supply line 18 that is common to all working spaces8, and to which a system pressure or high pressure is applied. This highpressure can be created e.g. using a pump 20.

Moreover, each working space 8 is connected via a drain valve 22 to alow-pressure side drain line 24, which is likewise common to all workingspaces 8, and which leads into a tank 26.

As explained initially, drain valves 22 and inlet valves 16 are designedas electrically releasable and blockable non-return valves in theembodiment shown. In its home position shown, inlet valve 16 ispreloaded into a closed position via a not-shown spring, and can bemoved into an open position by applying current to a solenoid actuator28, thereby allowing the pressure medium to flow out of inlet line 18into particular working space 8. In its home position shown, drain valve22 is preloaded into an open position using a spring. By supplyingcurrent to solenoid actuator 30, drain valve 22 is moved into a blockingposition in which pressure medium cannot flow out of working space 8.Solenoid actuator 28, 30 is activated by a control unit 34 which is usedto set the above-described modes (full mode, partial mode, idle mode),and therefore the intake volume of the hydraulic motor is approximatelysteplessly adjustable, wherein pulsation can also be reduced to aminimum by activating valves 16, 22 in a suitable manner. According tothe invention, valves 16, 22 are activated depending on the rotationalangle of output shaft 12, the rotational angle being detected using anangle-of-rotation sensor 36 and reported via a signal line to controlunit 34. In principle, other characteristic data of the hydraulicmachine such as the torque acting on output shaft 12, the intake volumeof hydraulic motor 1, or the angle of rotation of the swash plate can betaken into account, of course, in the activation of valves 16, 22.

Cylinder drum 2, the swash plate, and output shaft 12 connected theretoare supported in a housing 38 of hydraulic machine 1. FIG. 2 shows anend-face end section of housing 38, in which output shaft 12 issupported via a not-shown bearing system. A bearing cover 42 is placedon end face 40—which is shown in FIG. 2—of housing 38. A stepped endsection of output shaft 12 enters a recess 44 of bearing cover 42, whereit is covered by a sealing bushing 46.

An axially projecting hub section 47, on which an annular base body 48is placed, is formed on above-mentioned stepped end section of outputshaft 12. The fit between hub section 47 and base body 48 is designedwith a high level of accuracy, thereby ensuring that base body 48 iscentered exactly. The rotational angle positioning of base body 48relative to hub section 46 of output shaft 12 is ensured by using one ormore location pins 50 and fastening screws 52 which preferably lie on acommon partial circle and extend through base body 48 and a region ofoutput shaft 12 in an axially parallel manner.

A Gray code track carrier and an incremental track carrier 54, 56 arefastened to base body 48, the axial extension of said track carriersbeing substantially less than that of base body 48. Gray code trackcarrier 54 is supported in the region of the end face of base body 48located at the bottom in FIG. 2, and incremental track carrier 56 issupported in the region of the upper end face of base body 48, andtherefore the end faces of the base body and respective track carrier54, 56 are approximately aligned. An incremental track 58 and a Graycode track 60 are formed on the circumferential surfaces of the two codetracks 54, 56.

The design of tracks 58, 60 will be explained with reference to FIG. 3.FIG. 3 shows the design of incremental track 58 and Gray code track 60.Incremental track 58 is subdivided into a total of 72 track sections 62,each having the same width, and each representing, in alternation, thenumber (bit) “0” or “1”.

Gray code track 60 shown at the bottom in FIG. 3 is subdivided into 36track sections 64; particular Gray code sections 66, 68, 70, etc. areobtained by designing these track sections accordingly, wherein thelight track sections stand for the number “0”, and the track sectionsmarked with an “X” stand for the number “1”, for instance. Therefore,when output shaft 12 rotates, incremental track 58 delivers an incrementhaving a resolution of 6°, while Gray code track 60 results in aresolution of 12°. By evaluating these two signals jointly, accuracy canbe increased further depending on the algorithm that is used. Gray codetrack 60 is selected such that only one bit ever changes for sensor 72when it is rotated by one track section 64.

Individual code tracks 62, 64 of incremental track 58 or Gray code track60 can be magnetized differently to depict the information “0” or “1”,or they can be composed of a material that changes a magnetic field. Asshown in FIG. 3, five sensors 72 are assigned to Gray code track 60, andtherefore a 5-bit code can be read by evaluating the sensor signals.Only one sensor 74 for reading a 1-bit code is assigned to incrementaltrack 58. It is characteristic of a Gray code for adjacent code wordsread by five sensors 72 to differ from each other by a single tracksection 64. Sensors 74, 72 are located in a holder 76 which is insertedinto an annular recess 78 in housing 38 in a non-positive or form-fitmanner. In the embodiment shown, holder 76 has a two-pieced design,including an inner ring 80 and an outer ring 82 enclosing inner ring 80in sections; sensors 72, 74 are supported between inner ring 80 andouter ring 82. According to FIG. 3, the five sensors 72 of Gray codetrack 60 are distributed evenly along the outer circumference of Graycode track 60, and therefore the angular distance between adjacentsensors 72 is 72°.

A unique feature of hydraulic machine 1 is that tracks 58, 60 run in apressure medium chamber filled with pressure medium. The optical sensorsthat are typically used could not be used in variants of that type, oronly with difficulty, and therefore the use of magnetic sensors ispreferred. Sensors 72, 74 are therefore designed such that they detect achange in a magnetic field induced by the rotation of tracks 58, 60, andthe corresponding signals can be used to calculate the absoluterotational angle position.

Since sensors 72, 74 are relatively sensitive, holder 76 is sealedagainst pressure medium chamber 84 using suitable sealing rings 86, 88.Outer ring 78 of holder 76 is preferably held in housing 38 in aform-fit manner.

In deviation from the embodiment described above, a plurality of sensors74 can be assigned to incremental track 58. It is also possible, inprinciple, to sample Gray code track 60 using another number of sensors72 in order to adapt the accuracy to the particular application.

The advantage of the design described above is high accuracy withadapted resolution. The rotational speed sensor can be used in thepressure medium, and installation is very easy since housing 38 can beaccessed from the end face. Furthermore, the solution according to theinvention is characterized by an extremely compact design; by usingincremental track 58, Gray code track 60, and a relatively large numberof sensors, the angle of rotation can be detected very exactly, thesignal transit time is short, and the signals are easily evaluated.

Since the two tracks 58, 60 are situated on one carrier (base body 48,code carriers 54, 56), the sensor system can be positioned in a veryflexible manner, and retrofitting can be easily performed.

Disclosed herein is a hydraulic machine having a variable intakevolume/pump capacity, the rotational angle position of which is detectedusing an angle-of-rotation sensor that includes a Gray code track and anincremental track.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in ahydraulic machine having a variable intake volume/pump capacity, it isnot intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

LIST OF REFERENCE CHARACTERS

-   1 Hydraulic machine-   2 Cylinder drum-   4 Cylinder bore-   6 Piston-   8 Working space-   10 Piston shoe-   12 Output shaft-   14 Control curve-   16 Inlet valve-   18 Supply line-   20 Pump-   22 Drain valve-   24 Drain line-   26 Solenoid actuator-   30 Solenoid actuator-   34 Control unit-   36 Rotational-speed sensor-   38 Housing-   40 End face-   42 Bearing cover-   44 Receptacle-   46 Sealing bushing-   47 Hub section-   48 Base body-   50 Location pin-   52 Fastening screw-   54 Gray code track carrier-   56 Incremental track carrier-   58 Incremental track-   60 Gray code track-   62 Track section-   64 Track section-   66 Gray code section-   68 Gray code section-   70 Gray code section-   72 Sensor-   74 Sensor-   76 Holder-   78 Annular receptacle-   80 Inner ring-   82 Outer ring-   84 Pressure medium chamber

1. A hydraulic machine having a variable intake volume/pump capacity,comprising: a cylinder (2); at least one piston (6); a plurality ofworking spaces (8) disposed in the cylinder (2), each of the workingspaces (8) being limited by the at least one piston (6) and at least onecylinder bore (4) in which the at least one piston (6) is accommodated;a reciprocating element (14), wherein the pistons (6) are supporteddirectly or indirectly on the reciprocating element (14), wherein saidreciprocating element (14) is configured to rotate relative to the atleast one piston (6), such that when the cylinder (2) rotates relativeto the at least one piston (6), the at least one piston (6) undergoes adisplacement that determines the volume of the working spaces (8); acontrol unit; high-pressure valves and low-pressure valves (16, 22),wherein said working spaces (8) are connected via said high-pressurevalves and low-pressure valves (16, 22) to high pressure and lowpressure, and to the control unit, wherein said control unit isconfigured to actuate the valves (16, 22) as a function of adisplacement of one of said at least one piston (6); anangle-of-rotation sensor (36), wherein said working spaces (8) arefurther connected to said angle-of-rotation sensor (36), wherein saidangle-of-rotation sensor is configured to detect the rotational angleposition of a rotating component (2, 14), wherein the angle-of-rotationsensor (36) has a Gray code track (60) and an incremental track (58),wherein at least one sensor (72, 74) is assigned to each of said Graycode track (60) and said incremental track (58).
 2. The hydraulicmachine according to claim 1, wherein the Gray code track and theincremental track (58, 60) are located on a circumference of a base body(48), and the sensors (72, 74) are distributed along the circumference.3. The hydraulic machine according to claim 2, wherein the Gray codetrack and the incremental track (58, 60) are offset in an axialdirection.
 4. The hydraulic machine according to claim 3, wherein aplurality of sensors (74, 72) is assigned to one track (58, 60).
 5. Thehydraulic machine according to claim 4, wherein five sensors (72) areassigned to the Gray code track (60), and one sensor (74) is assigned tothe incremental track (58).
 6. The hydraulic machine according to claim1, wherein the incremental track (58) has 72 track sections (62), andthe Gray code track has 36 track sections (64).
 7. The hydraulic machineaccording to claim 4, wherein the Gray code track (60) is selected suchthat a total of only one bit ever changes for the sensor (72) assignedto said Gray code track (6) when rotated by a track section.
 8. Thehydraulic machine according to claim 1, wherein the base body (48) isfastened to a drive shaft or output shaft (12).
 9. The hydraulic machineaccording to claim 8, wherein the sensors (72, 74) are accommodated on ahousing side in a holder (76).
 10. The hydraulic machine according toclaim 1, wherein the Gray code track (60) and the incremental track (58)run in the pressure medium.
 11. The hydraulic machine according to claim1, wherein the angle-of-rotation sensor is a magnetic sensor.
 12. Thehydraulic machine according to claim 9, wherein the holder (76) issealed against a pressure medium.
 13. The hydraulic machine according toclaim 8, wherein the base body (48) is has an end face, wherein saidbase body (48) is fastened on the end face to the drive shaft or outputshaft (12) and is covered by a housing cover (42).
 14. The hydraulicmachine according to claim 1, wherein said hydraulic machine has anaxial-piston design or a radial-piston design.